LOS ANGELES, April 7 (UPI) -- Seven years after The Sopranos left the airwaves with a record-breaking finale, HBO has another bonafide mega-hit on its hands.

Game of Thrones' fourth-season premiere drew 6.6 million viewers on Sunday night, the network's largest audience since the Sopranos series finale in 2007.

Those are huge numbers compared to season three premiere, which drew 4.4 million viewers, proving that the show's audience is growing.

The ratings also help justify Game of Thrones' mind-boggling production costs. Its actors film on location in three countries, and its first season cost $60 million.

Despite Sunday night's success, the network does have to work on technical issues with its online-streaming service, HBO Go, which had trouble handling the number of people trying to stream the premiere at the same time.

HBO Go crashed for two hours during the 9 p.m. telecast, just as it did during the True Detective finale last month.

"HBO Go did experience issues due to overwhelming demand around the premiere of Game of Thrones," the network said during the telecast. "The service has returned to several platforms and we are working hard towards full recovery, which we expect soon."

Looks like there's trouble in the realm. Apologies for the inconvenience. We'll be providing updates, so please stay tuned. #GameofThrones

United Press International is a leading provider of news, photos and information to millions of readers around the globe via UPI.com and its licensing services.

With a history of reliable reporting dating back to 1907, today's UPI is a credible source for the most important stories of the day, continually updated - a one-stop site for U.S. and world news, as well as entertainment, trends, science, health and stunning photography. UPI also provides insightful reports on key topics of geopolitical importance, including energy and security.

A Spanish version of the site reaches millions of readers in Latin America and beyond.

UPI was founded in 1907 by E.W. Scripps as the United Press (UP). It became known as UPI after a merger with the International News Service in 1958, which was founded in 1909 by William Randolph Hearst. Today, UPI is owned by News World Communications.